# Will Earth rotate backwards in the future?

Hello recently I heave heard the earth will eventually start rotating in the opposite direction (ie sunrise from the west) . I am not sure if this is true, but a lot of sites are claiming it to be true, they say that the earth's rotation is slowing down slowly, and it will eventually stop and start rotating in the opposite direction, please let me know if this is true or not as I do not have much knowledge in astronomy.

EDIT:

Some of the sites that claim this event to be true, explain it in this way - they say "The earth is slowing down every year, so much so that when it first started spinning each day was only 4 hours but now it's 24 hours, a day will come when the earth will stop rotating and it will behave like a spring and then it will start rotating in the opposite direction (they don't mention if humans will be alive till that day or not) "

Here are the sources that led me to consider the possibility of this event-

• If this is a genuine question, please just forget. Jan 7 '21 at 10:58
• If there are "many sites", you can surely provide sources (which are not of the esoteric type) Jan 7 '21 at 11:41
• When you hear things like this, try to imagine how it would work - what it would take. Use things that you do know about to help you. Imagine, for instance, taking a ball and spinning it on a table, floor, or your finger. The ball will stop moving after some time, due to forces acting upon it. Does the ball at this point then begin rotating in a reverse direction? Why / why not? What does it take for that to happen? And what about a heavier ball of the same size? Spin both at the same time, which stops first, and why? etc... Jan 8 '21 at 1:10
• I vote to reopen. The OP has a valid, focused question. The source of the claim is not relevant. We know that tidal locking is a thing, an answer would explain why the rotation can't reverse. It would not be easy to research an answer to this. We need to be more open to newbie questions. Jan 8 '21 at 12:13
• @planetmaker i edited the post and added the sources. Jan 11 '21 at 10:20

No, the Earth will not start to rotate in the opposite direction. Ever.

The reason Earth maintains its direction of rotation is conservation of angular momentum. Just like a moving body resists changes in velocity because it has linear momentum, a rotating body will resist forces that try to change its rotation state. Angular momentum can be moved around in a composite system (consider a figure skater pulling in her arms while spinning), but it doesn't disappear unless there is a lot of friction. Which space lacks.

There is a grain of truth in the confused articles that led to the question: Earth is losing some angular momentum over time. Most of this is due to tidal interactions with the moon. When the moon formed Earth rotated much faster and the moon was close. Mutual gravitation caused tides that made some of the angular momentum transfer from Earth to the moon, slowing the rotation of both (to the extent the Moon now only turns one face towards the Earth, tidal locking) and giving the moon more angular momentum in its orbit, making it move outwards at a very slow rate. There are also tides from the sun (and other planets) but they are too small to matter here.

In reality, the sun will become a red giant in 5 billion years and expand, ending the story of the Earth and moon (ironically in this context, likely by tides dragging in Earth into the sun when it gets close enough to the surface). But if we ignore that, what would happen?

As the Earth's rotation is slowed by lunar tides, eventually it would become tidally locked to the moon in about 50 billion years. The moon would always stay over the same spot, visible only from one hemisphere. But Earth, like the moon today, would also continue to rotate around its axis. It is just that the "day" would be more than a month (about 47 days), corresponding to one full rotation of the Earth-moon system. But the direction would be the same as now, since the moon is moving around the Earth in the same direction as Earth is rotating.

At this point there would still be some loss of angular momentum due to solar tides, so over very long time periods (about 50 billion years more) the Earth and moon would slowly orbit closer and closer. Eventually they would merge into an (again) somewhat fast spinning body (still moving in the same direction!)

In the really long run tidal forces would slow this rotation so the big planet would be tidally locked to the sun. But again, the one-year rotation of the planet would be in the same direction as now.

There is a lot of nonsense claimed on the Internet. Learn the basic laws of physics like conservation of energy and momentum, get used to do rough calculations, and you can usually see through it quickly.

There is a lot of confusion in those articles.

The headline though is The Earth won't start rotating backwards and The sun won't rise in the West

1. Yes Mars and the other planets do move retrograde against the stars. This happens once every year-and-a-bit, and is a perspective effect. The Earth moves faster than Mars and so it can overtake it. When Earth overtakes Mars, it appears to be going backwards. But to be clear Mars never actually goes backwards, and The orbit of the Earth never goes backwards. So finally The Sun will not rise in the west. The rest of the first article is just how this would confirm prophecy, and contains no astronomy.

2. Is a copy-and-paste combination of 1 and 3

3. Yes, the Earth's magnetic poles do sometimes "flip", and quite quickly on a Geological scale, taking only a few thousand years. There is some reason to think that a flip might occur in the next 100,000 years or so. There is no particular reason to believe that a flip is imminant. During a flip the magnetic field would weaken, and there would be less protection from the sun, but in previous flips, exactly 0 animals went extinct as a result of the flip. And even if the magnetic poles flip, the rotational poles stay the same. So The Sun will not rise in the West

4. This article is a "What if". It considers various effects of the Earth changing direction. It states "the earth is not likely to spontaneously change directions" This might be the understatement of the decade. It is absolutely impossible for the Earth to change direction unless willed to by God. Nothing physical do this: not man, nor asteroid impact, nor aliens.

In short these are three unreliable sources. Please just forget.

• Respectfully, I think we should leave "God's will" out of Astronomy Stack Exchange. We don't all share the same God belief, and I think it distracts us from the scientific arguments. Jan 11 '21 at 18:39
• It is highly relevant to the OP's question; if you see the links 1 it is about how this will be a fulfillment of prophesy. Whether you believe in God or not, I stand by the fact that It is absolutely impossible for the Earth to change direction unless willed to by God. If you believe in an all powerful god or gods, then you believe that god can do this. If you don't then I claim it is completely impossible. I could have included "magic" but I thought this would be flippant in the context in which the OP asked the question. Jan 11 '21 at 18:46

## Almost certainly not.

All available information seems to indicate that the Earth will probably not reverse it's spin direction before it ends. However, we don't have absolute certainty of this.

Inner-planetary collisions

There are numerical simulations indicating the "Existence of collisional trajectories of Mercury, Mars, and Venus with Earth" within 5 Gyr time-scales, published in Nature by Laskar and Gastineau 2009. These are based on the possibility of potential resonance orbits of the inner planets with Jupiter. Laskar was influential in showing that the Solar System is a mathematically chaotic system on large time scales. While the probability of inter-inner-planetary collisions was extremely low according to their simulations, $$unlikely \ne impossible$$. For certain grazing impacts, "angular momentum dominates" according to Elkins-Tanton and Weiss 2016 as shown in one of the excellent figures from their paper:

A sufficiently energetic inter-planetary collision could certainly change Earth's spin direction and either merge, graze, or potentially strip the mantle.

Exoplanetary collisions

Also, I don't think we can rule out the possibility of a near miss of our Solar System with another stellar system within the Milky Way. We know that there are some stars in retrograde galactic orbits that cross the Sun's prograde orbit around the Milky Way. If our Solar System was to pass through the stellar system of a retrograde star, an Earth collision with an exoplanet would be possible.

Notes:

1. One could argue that after a planetary collision, the Earth's composition would be so changed that it would no longer be the Earth. We could consider another case in which our Moon was knocked out of Earth orbit by a collision. Then the obliquity of the Earth would vary up to about 85 degrees according to Laskar et al.. If another smaller Earth impact collision tipped the obliquity past 90 degrees, the Earth would indeed be spinning the opposite direction without much change to its composition.

2. The sources linked by the OP are not scientifically credible, but that doesn't mean we can rule out the possibility of their conclusions. Astronomy is still an incredibly vibrant and open field with many unanswered questions. I don't think we can be 100% certain that the Earth's spin direction will never change when we don't have a universally accepted explanation for Venus's retrograde rotation.

3. I disagree with the heavy downvoting of the OP's question. They edited their post by adding links and their question is valid.